Slow (0.7–2 Hz) and fast (2–4 Hz) delta components are differently correlated to theta, alpha and beta frequency bands during NREM sleep

Objectives: Spectral power of 40 all-night sleep EEGs (Cz-Pz bipolar lead) recorded in 20 healthy young subjects was calculated after normalization on 30-s consecutive epochs by means of an autocorrelation method based on a 15-order autoregressive model. Methods: The spectral parameters were calculated for the 7 main EEG bands: slow delta (0.7–2 Hz); fast delta (2–4 Hz); theta (4–8 Hz); alpha (8–12 Hz); sigma (12–16 Hz); beta1 (16–35 Hz); and beta 2 (>35 Hz). Results: Strong negative correlations were found between power in the fast delta and either the alpha or the beta bands and between slow delta and theta bands, whereas the two delta bands showed little correlation with each other. Conclusion: The possibility that theses different relationships of slow and fast delta components with other frequency bands might reflect the neocortical or the thalamocortical origin of the delta waves is discussed.